The Biomechanics Research Group was founded in 1980 by Ulrich Witzel. Since then, it has been involved in the development of endoprostheses and the biomechanics of the musculoskeletal system. This has led to close cooperation not only with medical scientists and biologists, but also with paleontologists who are researching the development in the vertebrate skeleton. The Biomechanics Research Group uses the finite element method (FEM) as well as multibody simulation (MBS) to provide insights into evolutionary events and ontogenetic processes of living organisms. In addition to the analysis of biological and engineering constructs (FESA), virtual syntheses (FESS) are applied to investigate and demonstrate the relationships between forms and their functions. Current research is extending FESS to simulate growth and healing processes, taking into account time-dependent biological processes.
Finite Element Structure Analysis (FESA)
The core competence of the Biomechanics Research Group is the interdisciplinary application of the finite element method with the software ANSYS. This numerical computational method of engineering is used to answer medical, biological and paleontological questions. In the field of deductive analysis, mechanical states such as stresses in computer models of bones, joints or implants are calculated. In addition to solid bodies, the dynamic behavior of fluids, such as in flow simulations of the underwater flight of Plesiosaurus, or gases, as in the study of sauropod respiration, can also be modeled.
One focus in the field of medicine is the calculation and optimization of implants in orthopedics and trauma surgery. Special milestones are the development of a new generation of hip endoprostheses and a durable total knee joint for juvenile bone tumor patients as well as the optimization of acetabular cups and stems. Furthermore, developments and improvements of orthoses and cruciate ligament replacement procedures are worth mentioning as well as contributions to the understanding of accident mechanisms of pelvic ring fractures or the etiology of Perthes disease.
Through the study of structures in biology and paleontology, insights can be gained into the relationship between form and function and biomechanical laws. In basic research, extensions and quantifications of Wolff's law of transformation of bones and the further development of the tension chord principle into a comprehensive algorithm for bending minimization could thus be realized. Three-dimensional stress analyses of complex skulls under functional loading demonstrated compressive loading of the calvaria by the falx cerebri and tentorium cerebelli. Also, in the understanding of tooth suspensions, which is important for the development of dental implants, various analyses showed compressive stress application into the jawbone by passive collagenous tension cords. Furthermore, a previously unknown active bite-synchronous tension chord in the form of a long bite muscle tendon was found in long crocodile snouts to minimize bending of the jaws.
Finite element analyses are flanked by use of software to generate computer models from CT and MRI data (ScanIP), multibody simulations, and CAD applications.
Finite Element Structure Synthesis (FESS)
Following the postulate "form follows function", an inversion of the FESA approach was developed by Professor Witzel as virtual Finite Element Structure Synthesis (FESS). This method assumes the energetically reasonable lightweight construction of the skeletal system, which ensures the necessary bending minimization through its compression structure and tension chord systems. Bending-minimized compressive structures are the prerequisite of lightweight construction in zoology and engineering.
From an unstructured homogeneous build space, a specific functional load is iteratively determined to be mechanical if the synthesis result matches the bone or its mineralization in shape and structure. The focus is on the virtual synthesis of skulls, for example of the Neanderthal or of sauropods. Using older or younger finds of the same species and the corresponding iterative load determinations, an insight into the phylogeny of these creatures can be gained.
Syntheses are not limited to bones. For example, the formation of the three-dimensional cruciate ligaments from stem cells in the early embryonic knee joint can also be synthesized by movements in utero. This results in the kinematic design of a coupling cam mechanism that enables roll-slide motion in the reality of a knee joint and whose traction structures are also mechanically determined.
The extension of FESS to include time-dependent, mechanically determined processes enables the four-dimensional synthesis of growth, functional adaptation and healing. Based on causal histogenesis, the course of fracture healing can be simulated preclinically to optimize implants and rehabilitation plans. Current applications in the field of pediatric orthopedics simulate the development, treatment and consequences of deformities such as knock knees and bow legs (genu valgum/varum) or hip dysplasia. The focus is on linking both syntheses to simulate fracture healing and its influence on growth in fractures in children.
While the focus of the Biomechanics Research Group is on computer-aided simulation (in silico), the entire spectrum of experimental biomechanical methods can be covered (in vitro/ex vivo/in vivo) in projects with national and international scientific and clinical partners. These include histology, dissection, molecular biological methods or bioreactors for tissue engineering. Clinical collaborations include surgical assistance in orthopedic procedures and the possibility to record ground reaction forces in stance and gait with a force measurement platform. Furthermore, the chair workshop and the possibility for additive manufacturing are available.
The funding by the German Research Foundation (DFG) is of particular importance. This includes Professor Witzel's many years of work in DFG Research Group 533 "Biology of the sauropod dinosaurs: the evolution of gigantism" as well as funding for various projects of his own. Currently, the DFG is funding the project "Preclinical computer simulation of fracture healing in children".